Molecular Epidemiological Surveillance of Plasmid-Mediated Colistin Resistance Gene mcr-1 in Escherichia coli from the Carriage in Healthy Humans across China, 2016-2024

Abstract: OBJECTIVE This study aims to long-term monitor the prevalence and molecular characteristics of the mcr-1 gene in human-derived Escherichia coli. METHODS This study conducted long-term continuous monitoring of mcr-1 positive E. coli from the carriage in healthy humans across 30 provinces/municipalities in 2016, 2019, 2022, and 2024. MALDI-TOF/MS was used for strain identification and PCR amplification was utilized to screen the mcr-1 gene. Bioinformatics and statistical analysis were performed based on the result of susceptibility test and whole genome sequencing. RESULTS The study found that since the ban on colistin, the prevalence of the mcr-1 gene in E. coli significantly decreased from 15.0% in 2016 to 0.05% in 2024 (p<0.05). The resistant rate of mcr-1-positive E. coli to amikacin, cefotaxime, ciprofloxacin, aztreonam, and cefperidone/sulbactam significantly increased during 2016 to 2022. Plasmid diversity analysis showed that mcr-1-positive plasmids exhibit diversity in 2016., with IncI2 subsequently became the main plasmid type carrying mcr-1. The genetic environment analysis of the mcr-1 gene showed that the IncI2 plasmid retained the mcr-1-pap2 structure of transposon Tn6330 during evolution. CONCLUSION The prevalence of E. coli carrying mcr-1 gene in healthy human gut significantly decreased from 2016, while its resistant rate to some antibiotics significantly increased. The plasmids carrying mcr-1 were more concentrated, with IncI2 plasmid becoming the dominant plasmid, suggesting the necessity on monitoring the biological features and clinical hazard of mcr-1-positive IncI2 plasmid.